This invention relates generally to acoustic well logging and more particularly to the determination of the quality of the cement bonding of the casing to the formation in an oil or gas well.
In the completion of wells, casing is normally lowered into the well and a cement slurry is flowed down the casing and up the annular space between the casing and the wall of the well. The casing, when cemented into place, isolates the oil- or gas-producing formation from other formations surrounding the wellbore.
In some well completions, the cement bond between the casing and the formation surrounding the wellbore will contain undesirable defects which can permit undesirable fluid flow communication between the production formation and formations above or below the production formation. Acoustical noise logging of completed wells to determine the location of fluid flow thereinto is well known in the art. For example, in U.S. Pat. No. 2,210,417 to Kinley, leaks through or behind the well casing are located by determining the location of sound produced by liquid passing through openings in the casing or behind the casing. A sound detector is moved through a well and is connected to an uphole, indicating device or recording means. The intensity of sound of liquids passing through the casing is indicative of casing leaks, and location of such leaks is readily discernible from a graphical record of intensity versus the depth of the sound detector within the well. A similar method of detecting casing leaks is disclosed in U.S. Pat. No. 2,396,935 to Wahlstrom.